Akihide Hemmi

Development of a conductivity-based immunosensor for sensitive detection of methamphetamine (stimulant drug) in human urine

A simple immunosensor based on a conductivity method was developed for determination of methamphetamine (MA, a stimulant drug) in urine. Anti-MA antibody was immobilized onto the surface of a pair of platinum electrodes. The reaction of MA with the antibody causes a decrease in the conductivity of the anti-MA immobilized layer between the electrodes. A linear relationship was obtained between the conductivity and MA concentration in the range of 1-10 micrograms/ml. The method requires the sample to be rinsed with water on the electrodes after the immunoreaction. This detection system was applied to the determination of MA in urine and proved to be a useful and a simple detection technique of MA in forensic science in comparison with a gas chromatography-mass spectrometry method.

Application of semiconductor gas sensor to quality control of meat freshness in food industry

Abstract We have investigated the possibility of utilizng a semiconductor gas sensor for quality control of meat freshness in the food industry. A semiconductor gas sensor based on In 2 O 3 is exploited for detecting ethyl acetate, a typical flavour volatile component produced in the initial bacterial putrefaction of meat. Of the sensor elements examined, Rh-La 2 O 3 -In 2 O 3 is found to show excellent sensitivity and selectivity to ethyl acetate at 300 °C. The sensor response signal increases with increasing meat-storage time and reflects rather well the increase of bacteria determined by a conventional colony-counting method. The multiple correlation factor between both methods is 0.8.

Development of a chemiluminescence detector with photodiode detection for flow-injection analysis and its application to L-lactate analysis

A low cost chemiluminescence detector with a photodiode for flow-injection analysis (FIA) of l-lactate in food was developed for quality control in food industry. In this system, l-lactate is oxidized by the enzymatic reaction with l-lactate oxidase immobilized on the column to produce hydrogen peroxide. Then chemiluminescence caused by mixing hydrogen peroxide with the chemiluminescence reagent was detected by the photodiode. This light intensity was proportional to l-lactate concentration. For detecting weak chemiluminescence efficiently a flow-through cell of the detector was specially designed. A photodiode was used for the purpose of reducing the costs of FIA systems instead of a photomultiplier tube. As a result, a linear working curve was obtained from 10−7to 10−3 mol l−1l-lactate concentration. We applied the present system with a photodiode detector for food samples and compared the results with those obtained by the conventional HPLC method. The data obtained by the present FIA method were fairly in good agreement with those obtained by the conventional HPLC method. The correlation factor and regression line between both methods were 0.992 and Y = 1.07X-0.15, respectively. The present FIA system with the photodiode detector is available as a simple, easy-handling instrument for quality control in food industry.

Performance of an organic photodiode as an optical detector and its application to fluorometric flow-immunoassay for IgA.

The performance of an organic thin film photodiode (OPD), fabricated from a hetero-junction comprised of two layers of C(60) and a phthalocyanine-Cu(II) complex was evaluated by detecting the chemiluminescence generated from the reaction of luminol with horseradish peroxidase in the presence of H(2)O(2), and the fluorescence from resorufin, as an optical detector. The photocurrent of the OPD was linear with respect to the power of light from a commercial LED. The sensitivity of the OPD was sufficient for detecting chemiluminescence with a power 0.1μW/cm(2). The OPD was successfully used in a flow-immunoassay for IgA, a marker of human stress, in which a sandwich immunoassay was carried out on the microchip and the fluorescence from resorufin, produced by the enzymatic reaction, was detected. The detection limits for resorufin and IgA were 5.0μM and 16ng/mL, respectively. The photosensitivity of the OPD remained relatively constant for a minimum of one year.

A palm-sized surface plasmon resonance sensor with microchip flow cell

A small-sized surface plasmon resonance (SPR) sensor with a microchip flow cell has been developed for the purpose of enhancing the sensitivity of the SPR detector for low molecular weight compounds. This portable differential SPR detector consisted of an LED, two cylindrical lenses, a round prism, a divided mirror, a CCD, electronics, and a polydimethylsiloxane/gold microchip with two flow paths (10mm long, 1mm wide, 20-100mum deep). 3-Mercaptopropyltrimethoxysilane was used for sealing the microchip. The performance of the on-site orientated SPR detector was estimated using sucrose and IgA. A drastic change in the SPR intensity appeared. The depth of the flow cell was in inverse proportion to the SPR intensity. Compared to a conventional flow cell having the size of 10mm (L)x1mm (W)x1mm (D), its sensitivity to 10% sucrose and 0.9nM IgA increased about 11 and 39 times, respectively. This phenomenon seemed to be due to the increase in the substance on the SPR sensor based on its size effect. These results showed that the application of the microchip sensor for SPR measurement has the possibility for improvement of the SPR intensity for low molecular substances.

Flow injection analysis for residual chlorine using Pb(II) ion-selective electrode detector.

A simple flow injection analysis (FIA) system for residual chlorine in tap water has been developed by using a Pb(II) ion-selective electrode (ISE) detector. The method is based on a specific response of the Pb(II)-ISE to residual chlorine. The FIA system consists of a millivolt meter, a peristaltic pump, a Pb(II)-ISE detector and a recorder. A linear working curve between peak height and concentration of residual chlorine was obtained from 0.1 to 1 mg l(-1) for the developed FIA system. The relative standard deviation for repeated injections of a 0.2 mg l(-1) residual chlorine sample was 2%. The regression line and its correlation factor between the conventional o-tolidine colorimetric method and the present method were Y=0.75X+0.17 and 0.967, respectively, for this determination.

Flow immunoassay of trinitrophenol based on a surface plasmon resonance sensor using a one-pot immunoreaction with a high molecular weight conjugate

A surface plasmon resonance (SPR) immunosensor based on a competitive immunoreaction for the determination of trinitrophenol (TNP) is described. A goat anti-mouse IgG (1st antibody), which recognizes an Fc moiety of an antibody, was immobilized on a gold film of an SPR sensor chip by physical adsorption. A TNP solution containing a fixed concentration of a mouse anti-TNP monoclonal antibody (2nd antibody) and a TNP-keyhole limpet hemocyanin (KLH) conjugate was incubated in one-pot and introduced into the sensor chip. The TNP-KLH conjugate competes with TNP for binding with the 2nd antibody. The resulting complex of the 2nd antibody with the TNP-KLH conjugate was bound to the 1st antibody, which is immobilized on the sensor chip. The SPR sensor signal based on resonance angle shift is dependent on the concentration of TNP in the incubation solution in the range from 25ppt to 25ppb, and the coefficient of variation of the SPR signals for the 25ppb TNP solution was determined to be 13% (n=4). The experimental results for the adsorption constant of the 1st antibody on the sensor chip and the binding constant of the 1st antibody complex with the 2nd antibody are discussed, together with theoretical considerations.

Determination of hardness in tapwater and upland soil extracts using a long-term stable divalent cation selective electrode based on a lipophilic acrylate resin as a membrane matrix

A divalent cation-selective electrode, which utilizes a lipophilic resin as a matrix for the sensing membrane, and which has long-term stability has been developed. The sensing membrane is a lipophilic acrylate resin which is impregnated with a solution of 1-decylalcohol and the calcium salt of bis[4-(1,1,3,3-tetramethylbutyl) phenyl] phosphate at concentrations of 0.08 g ml(-1) each. The electrode exhibited nearly equal selectivity to Ca(2+) and Mg(2+) ions and could be used as a water hardness sensor. The electrode shows a Nernstian response with a slope of 29 mV decade(-1) to both Ca(2+) and Mg(2+) ions in the concentration range from 10(-5) M to 10(-1) M and could be used in the pH range from 3 to 10 for the determination of 10(-3) M Ca(2+) and Mg(2+) solutions. The initial performance of the electrode could be maintained for 1 year, since the lifetime test of the electrode was conducted in tapwater at a continuous flow rate of 4 ml min(-1). The hardnesses of tapwater and upland soil extracts were determined using the developed electrode and the analytical results were in good agreement with those obtained by chelatometric titration using an EDTA solution as the titrant. A coefficient factor of correlation 0.998 was obtained between the electrode method and titrimetry. The long-term stability of the electrode was found to be due to strong affinity of 1-decylalcohol to the lipophilic acrylate resin.

A surface plasmon resonance sensor on a compact disk-type microfluidic device

A surface plasmon resonance (SPR) sensor on a compact disk (CD)-type microfluidic device was developed to miniaturize the elements of a complete analytical system, pump and valves. The CD-type microfluidic device was fabricated by attaching a polydimethylsiloxane disk plate that contained microchannels and reservoirs to a flat polycarbonate disk plate that contained grating films with a thin layer of Au. The optical system of the SPR sensor and the theory for its operation are based on the principle of a grating coupled-type SPR. The sample and reagent solutions in the reservoirs on the CD-type microfluidic device were sequentially introduced into the detection chamber by centrifugal force generated by the rotation of the microfluidic device. The variation of resonance wavelength was dependent on the refractive index of the sample solution. This CD-type SPR sensor was successfully used in an immunoassay of immunoglobulin A (IgA). The anti-IgA, blocking reagent, sample and washing solution in the reservoirs were sequentially introduced into the detection chamber by changing the frequency of rotation of the microfluidic device. IgA in the sample solution was adsorbed to the anti-IgA immobilized on the Au thin layer in the detection chamber and was then detected by the SPR sensor.

An integrated enzyme‐linked immunosorbent assay system with an organic light‐emitting diode and a charge‐coupled device for fluorescence detection

A fluorescence detection system for a microfluidic device using an organic light-emitting diode (OLED) as the excitation light source and a charge-coupled device (CCD) as the photo detector was developed. The OLED was fabricated on a glass plate by photolithography and a vacuum deposition technique. The OLED produced a green luminescence with a peak emission at 512 nm and a half bandwidth of 55 nm. The maximum external quantum efficiency of the OLED was 7.2%. The emission intensity of the OLED at 10 mA/cm(2) was 13 μW (1.7 mW/cm(2)). The fluorescence detection system consisted of the OLED device, two band-pass filters, a five microchannel poly(dimethylsiloxane) (PDMS) microfluidic device and a linear CCD. The fluorescence detection system was successfully used in a flow-based enzyme-linked immunosorbent assay on a PDMS microfluidic device for the rapid determination of immunoglobulin A (IgA), a marker for human stress. The detection limit (S/N=3) for IgA was 16.5 ng/mL, and the sensitivity was sufficient for evaluating stress. Compared with the conventional 96-well microtiter plate assay, the analysis time and the amounts of reagent and sample solutions could all be reduced.